1. Field of the Invention
The present invention is directed toward a process and apparatus for removing ink from plastic materials, such as plastic films and food and beverage containers. In certain embodiments, the ink to be removed has been applied to the plastic material by dry offset printing, although other types of ink and printing processes may also be used.
2. Description of the Prior Art
The startup of a dry offset printing line, including the change-over from printing one type of image to another, is generally considered an art form as it involves a number of manual adjustments to the line including the positioning of the various plates and color usage. Further, it is not uncommon for any printing operation to produce misprinted items or have over-runs in terms of quantities of products printed. These operations typically result in the creation of 4-7% scrap product (based upon the total product to be printed). The scrap plastic is traditionally ground up and resold for non-food and beverage applications. As the cost of raw materials, particularly plastics, continues to rise, the production of high levels of scrap material can prove quite costly.
U.S. Pat. No. 5,830,836 is directed toward compositions and methods for removal of polymeric coatings, such as paint, enamel, lacquer, varnish, a sealant, or the like, from non-porous surfaces, such as metal, certain stone, acrylic siding, and may be the surface of an aircraft, a car, or a building. Particularly, a peroxide-based solution having a pH of about 6.5 to 11.0 is used. This solution may also comprise a surfactant such as between 1-5% by weight of a linear alkyl ethoxylate, and significant quantities of benzyl alcohol and various glycols. The solution is preferably mixed up just prior to use and remains useful for only about 24 hours.
U.S. Pat. No. 6,147,041 is directed toward a removable ink composition and a process for removing the ink from printed articles. The ink removal process generally comprises applying a 1-3% solution of sodium hydroxide at a temperature of 80-90° C. onto a plastic bottle, for example, containing an image printed thereupon. The solution is then permitted to contact the plastic substrate for 20-30 minutes.
U.S. Pat. No. 6,663,929 is directed toward removing ink from labels, made from a heat-shrinkable polymer film, by contacting the film with a hot alkaline solution (3% sodium hydroxide, at 90-95° C. for 30 minutes.
U.S. Pat. No. 6,803,085 is directed toward a method of removing an “ink-only” label from a plastic substrate without destructive treatment of the substrate. The label is removed by exposing the label and substrate to a pre-rinse solution comprising 1-5% sodium hydroxide at 60° C. Next, the substrate is soaked in a similar sodium hydroxide-based solution for between 40-110 seconds wherein the labels are completely removed. The substrate is then rinsed with 30° C. water.
U.S. Pat. No. 7,416,612 is directed toward a process for removing paint from a plastic substrate so that the substrate can be repainted for reuse. The process involves immersing the coated plastic substrate into a first aqueous fluid that contains benzyl alcohol, glycolic acid, sodium lauryl sulphate, 2-mercaptobenzothiazole, and xylene, and has a temperature of 140-180° F. After this immersion step, the plastic can either be rinsed off and reused, or it can be immersed in a second fluid comprising a blend of biodegradable, non-regulated solvents and emulsifiers, such as ethylene glycol, monoethyl or diethyl ether, and a dibasic ester.
As can be seen, a number of these references utilize caustic or hazardous compounds. Further, a number of the processes described the above references are quite time consuming. Accordingly, there is a need to develop a quick, safe, and bio-friendly way to de-ink plastic articles so that they may be reused. The present invention seeks to avoid use of hazardous chemicals by providing a method of de-inking plastic articles using a safe and bio-friendly solvent. Additionally, the present invention provides an apparatus that can de-ink plastic articles in a timely, efficient, and automated manner.